Only a limited number of molecules with demonstrated therapeutic value can be transported through the skin, even with the use of approved chemical enhancers. The main barrier to transport of molecules through the skin is the stratum corneum (the outermost layer of the skin).
Devices including arrays of relatively small structures are sometimes referred to as microneedles, microneedle arrays, micro arrays, micro-pins, or the like. These structures have been disclosed for use in connection with the delivery of therapeutic agents and other substances through the skin and other surfaces. These medical devices pierce the stratum corneum and form a plurality of microscopic slits or holes in the outermost layer of skin to facilitate the transdermal delivery of therapeutic agents through the skin. The devices are typically pressed or abraded against the skin in an effort to pierce the stratum corneum such that the therapeutic agents and other substances can pass through that layer and into the tissues below.
In some embodiments, the microneedle arrays include structures that have a capillary or passageway extending through the microneedle. This capillary or passageway enables the microneedle to deliver fluid therapeutic agents through the skin of a subject or to extract fluids through the skin from the subject.